This invention relates generally to support beams for a fire-rated suspended ceiling system and more particularly to an improved expansion relief section for such beams which is deformable under the application of expansion forces in the beam accompanying fire conditions to accommodate such expansion.
In general a beam for a fire-rated suspended ceiling structure has an inverted-T construction and includes a central web having a bulb at the top and a pair of oppositely disposed flanges at the bottom for supporting ceiling tiles or the like. Expansion joints or sections have been fabricated into the beams to accommodate for expansion of the beam when it is subjected to high temperature accompanying fire conditions. While the prior art has disclosed various types of fire-rated beam expansion systems, they have left something to be desired. The prior art ceiling suspension systems offering such expansion relief create a weakness in the support beams and to overcome that weakness isolate the required expansion to a minimum number of expansion relief points. The present invention overcomes the weakness in such structures by removing less material. By keeping more of the structure intact, more expansion relief points can be provided thereby providing expansion where it is needed. Another common failure in prior systems is the risk of the tile supporting flange buckling upward thereby limiting the beam expansion to less than is expected. The present invention eliminates the risk by providing means of positive force downward on the tile supporting flange to insure full expansion potential.
In the prior art beams, while various arrangements have been made in both the web and the bulb of the beam such arrangements have tended to weaken the beam. It is extremely important that ceiling the supporting grid structures maintain their integrity under abnormally elevated temperatures, such as accompanying the fire. Under these high temperature conditions, metallic grid members, which generally are fixed at their end points, expand and buckle whereby the supported ceiling tiles are displaced and sometimes tilted to such an extent that they drop through the openings formed by the intersecting grid members. As a result the effectiveness of this suspended ceilings as a fire barrier is destroyed and the overhead ceiling and related support structure is exposed to fire whereby such fire can spread more easily and rapidly through the entire structure.
The disadvantages of the prior art are overcome by the present invention which not only provides a strong supporting beam structure under normal conditions but when the beam is subjected to expansion forces accompanying fire conditions the expansion forces are relieved on the beam without substantial twisting of the beam thereby avoiding displacement of the support for the ceiling tiles.